Tungsten-halogen incandescent lamps are well known. A major advantage of tungsten-halogen lamps is improved lumen maintenance made possible by the halogen cycle which captures evaporated tungsten and returns it to the filament thereby virtually eliminating blackening of the bulb walls. The halogen cycle is sustained by surrounding a tungsten filament with a special atmosphere at appropriate pressure containing one or more halogens within a hermetically sealed envelope or capsule. Because of the virtual absence of wall blackening, the halogen capsule may be quite small. An outer envelope enclosing the halogen capsule provides the inner capsule with structural integrity, thermal and electrical isolation, and other important benefits which contribute to the feasibility of the lamp as a commercial and consumer product.
Under the existing art, the manufacture of a tungsten-halogen lamp typically involves the following steps. A halogen capsule having two lead-in wires is mounted on a glass stem support. The capsule and stem are inserted into the outer envelope. The glass stem support is flame sealed to the glass outer envelope. The outer envelope is evacuated, a desired fill gas may be introduced into the outer envelope, and the outer envelope is hermetically sealed. A lamp base is mounted on and cemented to the neck of the outer envelope. One of the capsule lead-in wires is soldered to the insulated tip of the base. The second lead-in wire is soldered to the outer shell of the base.
The described manufacturing process is relatively costly. The fabrication of a hermetic seal between the lead-in wires and glass stem and between the stem and outer envelope requires considerable technological skill and quality control.
The lighting industry is searching for a replacement for the Edison-type incandescent lamp which is currently the most popular type of lamp sold in the consumer market in the United States. Tungsten-halogen lamps, because of their superior performance characteristics, are being carefully considered by various lamp manufacturers as a replacement for the standard incandescent lamp. However, the cost of manufacturing a tungsten-halogen lamp under the existing art is significantly higher than that of the standard lamp. Consequently, there would be only a weak incentive for the consumer to purchase a tungsten-halogen lamp instead of the standard lamp. A tungsten-halogen lamp which can be provided at substantially less cost would constitute an advancement in the art.